A compound which releases a photographically useful group counter-imagewise, i.e., positive acting compound can be expected to exhibit various functions unprecedented for the prior art precursors in a silver halide photographic material, has been intensively studied.
Proposed examples of positive acting compounds include the passive compounds described in U.S. Pat. Nos. 4,199,354 and 3,980,479.
Such a compound can undergo an intramolecular nucleophilic reaction in the presence of an alkali in a reduced state to release a photographic reagent. Such a compound also undergoes oxidation via a redox reaction in a light sensitive material. This redox reaction serves to lower the rate at which the photographic reagent is released. By utilizing such a property, a photographically useful group can be imagewise released. However, since oxidation and alkaline hydrolysis compete with each other, such a compound is disadvantageous in that a shift in the timing between the two reactions causes a generation of fog or deterioration in discrimination. Furthermore, such a compound is unstable Thus, positive acting compounds have many disadvantages.
In order to eliminate the above disadvantages a positive acting compound in the form of an oxidation product which can undergo a redox reaction with a reducing agent to release a photographically useful group has been proposed. A great number of positive acting compounds have been developed.
Examples of these positive acting compounds include positive acting compounds which undergo intramolecular displacement reactions after being reduced to release a photographic reagent. Such compounds are disclosed in U.S. Pat. Nos. 4,139,389, 4,139,379, and 4,564,577, JP-A-59-185333, and JP-A-57-84453 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Positive acting compounds which undergo intramolecular electron transfer reactions after being reduced to eliminate a photographic reagent include those disclosed in U.S. Pat. No. 4,232,107, JP-A-59-101649, JP-A-61-88257, and Research Disclosure, No. 24,025, IV, 1984.
Furthermore, positive acting compounds which undergo bond cleavage by reduction to release a photographic reagent have been studied.
Examples of positive acting compounds utilizing such a reaction include compounds utilizing nitrogen-sulfur bond reduction cleavage as disclosed in German Patent No. 3,008,588, compounds utilizing nitrogen-nitrogen bond cleavage as disclosed in U.S. Pat. No. 4,619,884 and .alpha.-nitro compounds which undergo carbon-hetero atom single bond cleavage after receiving electrons to release a photographic reagent as disclosed in German Patent No. 3,207,583. Other examples of such compounds include compounds utilizing carbon-hetero atom bond reduction cleavage such as geminar dinitro compounds which undergo nitrogen-nitrogen (nitro group) bond reduction cleavage which results in the .beta.-elimination of a photographic reagent as described in U.S. Pat. No. 4,609,610. Further examples of compounds utilizing carbon-hetero atom single bond reduction cleavage include nitrobenzyl compounds disclosed in U.S. Pat. No. 4,343,893.
In recent years, a compound as described in European Patent No. 2,220,746A2 and Koaki Giho 87-6,199 has been developed as a positive acting compound which exhibits better stability and higher activity during processing and also exhibits a higher degree of freedom of design and tolerance in the preparation of a photographic element.
Compounds having such functions have many advantages. It is preferable that the properties and capabilities of the positive acting compound be improved so as to further increase the degree of freedom of design and tolerance in the preparation of a photographic element (material). It is further preferable that the photographic element be provided with a compound having a higher stability before and after processing. It is also preferred that a better means be provided to control the release of the photographically useful component.